Yields on 10-year and 30-year Treasury securities are typically used to set long-term mortgage rates. Loans with short initial terms (1-, 3-, and 5- year
ARMs, e.g.) are pegged to shorter-term securities. So when bond yields drop, typically, conventional mortgage rates fall as well (see historical graph below).
Conversely, when yields rise, so do mortgage rates. Why? If a lender chooses to sell your mortgage loan to an investor, the lender will likely use Treasury
yields as a benchmark for value.

The Yield Curve - the yields of U.S. Treasury bill, notes and bonds - can reveal a lot about markets. The "usual shape" of the yield curve is
positive; that is, with short term rates lower than long term. Almost all recessions have been preceded by an inverted curve (with short term rates higher than
long term), and such a curve usually points to lower rates in the future. A steeply positive curve points to future higher rates.